Hi Birdboot,
I also have family buried in Kilmalieu burial ground. Details for deaths around that time are not available, as you know.
I decided to have another dig around on the net and Googled " Kilmalieu burial ground"
Somebody has made available - on Flickr - photos of Kilmalieu and among them is a photo of the burial stone of your Catherine Ross , wife of Robert Mc Kellar , Innkeeper ---
Hopefully, you may be able to contact the person who took the photos and get copies.
Let me know how you get on, Regards, Jean